How do empty string and null differ in the context of databases?

In the context of databases, null and an empty string ("") have different meanings:

• null means the absence of a value, i.e., the field contains no data. It is a state where the value is unknown or not set.
• Empty string is a specific value indicating that the field contains a string of length 0 characters.

For example, in a user table, the "middle name" field can be null if the user did not specify a middle name, while an empty string can mean that the middle name is absent or not applicable.

When querying and filtering, it is important to consider this difference, as null and an empty string are handled differently (for example, WHERE field IS NULL and WHERE field = '').